1. Field of the Invention
The present invention relates to water based highway or roadway paints that contain a luminescent substance, which does not require an organic solvent, a colored paint dispersion and a polyurethane resin which is water miscible, and which imparts an extended surface life under normal traffic conditions.
2. Background Art
It is presently desirable to produce luminescent highway paints whose compositions do not require organic solvents whose vapors are undesirable when released to the atmosphere. U.S. Pat. No. 4,172,063 discloses an abrasion resistant reflective marking composition containing cement a fluorescent pigment, silica, glass fibers and a filming bonding acrylic polymer agent. This composition is, however, not environmentally friendly.
The term "luminescence" as used in this specification and in the appended claims is meant to be that property of a material which causes visible light to be continued to be emitted after an exciting light source has been removed as well as that property of a material to glow under a source of light of low visibility and suitable wavelength. U.S. Pat. No. 223,050; 274,415; 1,407,534 and 1,637,963 disclose the use of luminous (phosphorescent) compositions in paint, enamels, and as a coloring on paper. A paint mixture with an acrylic vehicle but having an alkaline earth phosphor other than zinc sulfide which could be modified by replacing its alkaline earth phosphor with zinc sulfide to obtain a preferred phosphorescent paint is described in U.S. Pat. No. 2,436,182. All of these cited references are incorporated in their entirety herein.
As is well-known, fluorescent paints when excited by a source of light produce an emission of light but the light emission is limited to the period of excitation. Such paints can be selected to provide a clay time coloration which will demarcate and emphasize the highway edges and median traffic divider stripes.
Phosphorescent paints on the other hand, once they have been excited, remain luminous with a soft, slowly decaying emission or radiation. Such phosphorescent paints can generate a useful level of luminous flux for periods of time (even several hours) when exposed to sunlight or artificial light (such as from headlights of automobiles) in the dark of night. After an initial exposure to a light source, luminescence can be restored by once again exposing the paints to either a natural or an artificial light. Thus, highway paints have incorporated fluorescent or phosphorescent paint to demarcate the edges of highways and the median line of the highway to differentiate the different directions of the highway vehicles. Previously highway paints, due to chemical attack by the atmosphere on the phosphor, lose their capacity to phosphorescence in six to twelve months.
However, it is necessary that a highway paint have the following characteristics such as ease of application, short track time, long wearability and suitable luminescence. Of these, the most difficult to achieve is long wearability under normal traffic conditions.
Accordingly, it is a principal object of the present invention to provide a highway or roadway paint that is environmental protective, luminescent (phosphorescent and/or fluorescent) and has increased roadway life and durability.
Other objects of the present invention, as well as particular features, elements, and advantages thereof, will be elucidated in, or be apparent from, the following description of the invention.